Briggs and Stratton 303777

Briggs and Stratton 303777The Briggs and Stratton 303777 Vanguard is a 495 cc (30.2 cu·in) V-twin air-cooled four-stroke internal combustion gasoline engine, manufactured by Briggs and Stratton.

The B&S 303777 engine has an OHV (over-head valve) design and a vertical PTO shaft. This engine is equipped with float type, side-draft carburetor and a magneto electronic ignition system. The B&S 303777 engine used a full pressure lubrication system with spin-on oil filter.

The cylinder bore is 68.0 mm (2.68 in) and the piston stroke is 66.0 mm (2.6 in). The compression ratio rating is 8.2:1.

This engine produced 16.2 PS (11.9 kW; 16.0 HP) at 3,600 rpm of horsepower.

The breakdown of the engine code is as follows:

  • 30 – Displacement
  • 3 – Basic design series
  • 7 – Vertical PTO-shaft
  • 7 – Plain bearing, Pressure lubrication
  • 7 – Electric starter

General information

Engine Specifications
ModelB&S 303777 Vanguard
Type4-stroke, L-head, V-twin
Displacement495 cm 3 (30.2 cu-in)
Max. horsepower16.2 PS (11.9 kW; 16.0 HP) at 3,600 rpm
Max. torque
Fuel systemFloat type, side-draft carburetor
Cooling systemForced-air
Ignition systemElectronic
Lubricating systemFull pressure lubrication with spin-on oil filter
Starting systemElectric starter
Fuel usedGasoline
Fuel tank capacity

Cylinder Block and Head

Cylinder block
Compression ratio:
Bore x Stroke68.0 mm X 66.0 mm (2.68 x 2.60 in)
Sleeve internal diameter68.000-68.030 mm (2.6772-2.6783 in)
Number of piston rings (compression / oil):2 / 1
Side clearanceTop0.045-0.076 mm (0.0018-0.003 in)
Second0.045-0.076 mm (0.0018-0.003 in)
Oil0.110-0.150 mm (0.0043-0.0059 in)
Ring end gapTop0.200-0.400 mm (0.0079-0.0157 in)
Second0.200-0.400 mm (0.0079-0.0157 in)
Oil0.200-0.400 mm (0.0079-0.0157 in)
Connecting rod small end ID17.090-17.100 mm (0.6728-0.6732 in)
Piston pin outer diameter17.070-17.080 mm (0.672-0.6724 in)
Cylinder Head
Valve Arrangement:OHV
Valves:4 (2 per cylinder)
Valve steam diameterINTAKE5.950-5.960 mm (0.2343-0.2346 in)
EXHAUST5.940-5.950 mm (0.2339-0.2343 in)

Tightening torque

Tightening torque specs
Alternator (to cylinder)2.0 Nm; 1.5 ft·lb
Air cleaner base (to carburetor)7.0 Nm; 5.2 ft·lb
Air cleaner support bracket7.0 Nm; 5.2 ft·lb
Alternator2.0 Nm; 1.5 ft·lb
Armature3.0 Nm; 2.2 ft·lb
Blower housings7.0 Nm; 5.2 ft·lb
Back plate7.0 Nm; 5.2 ft·lb
Breather3.0 Nm; 2.2 ft·lb
Carburetor to manifold7.0 Nm; 5.2 ft·lb
Connecting rod13.0 Nm; 6.9 ft·lb
Crankcase cover17.0 Nm; 12.6 ft·lb
Cylinder head19.0 Nm; 14.1 ft·lb
Cylinder shield7.0 Nm; 5.2 ft·lb
Exhaust manifold17.0 Nm; 12.6 ft·lb
Flywheel nut175.0 Nm; 129.6 ft·lb
Fan Retainer17.0 Nm; 12.6 ft·lb
Governor lever nut8.0 Nm; 5.9 ft·lb
Governor control bracket16.0 Nm; 11.9 ft·lb
Intake manifold to cylinder head16.0 Nm; 11.9 ft·lb
Oil pump7.0 Nm; 5.2 ft·lb
Rewind starter (to blower housing)7.0 Nm; 5.2 ft·lb
Rocker arm lock nut7.0 Nm; 5.2 ft·lb
Rocker arm stud11.0 Nm; 8.2 ft·lb
Starter motor16.0 Nm; 11.9 ft·lb
Starter motor thru bolts6.0 Nm; 4.4 ft·lb
Valve cover3.0 Nm; 2.2 ft·lb

Service Information

Max speed3,600 rpm
Valve clearance
Intake valve clearance0.10-0.15 mm (0.004-0.006 in)
Exhaust valve clearance0.10-0.15 mm (0.004-0.006 in)
Oil system
Oil typeAPI SF, SG, SH, SJ or higher
Recommended oil Summer: SAE 30, 10W-30
Winter: SAE 5W-30
Oil capacity (with filter)1.65 L (1.74 US. qt, 1.45 Imp. qt.)
Ignition system
Spark plugChampion RC12YC
Spark plug gap0.7-0.8 mm (0.0276-0.0315 in)
Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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  1. Where do I find the silly secret compression nos. for the Briggs & Stratton Model 303777 16 hp v-twin engine. I need to check its condition. Does it have a compression release for starting. How does that affect the cranking compression nos.? Thanks

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